Polymer used to make fluorosilicone rubber is made by the specialized ring opening polymerization of 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane, hereinafter fluoro cyclic trimer. Fluoro cyclic trimer is commercially produced in a cracking process where methyltrifluoropropylsiloxanes are heated to temperatures in excess of 200.degree. C. in the presence of a rearrangement catalyst and the relatively lower boiling cyclic trimer is fractionally distilled from the reactor at high purity. The process produces fluorosilicone cyclic trimer at a slow rate that requires long contact times between the siloxane mass and the strong base typically used as a cracking catalyst. These conditions of cracking cause side reactions between the siloxane mass and the catalyst.
The cracking process can be operated as either a one step process where pure fluoro cyclic trimer is taken from the top of a fractionating column attached to the reactor, or a two step process, i.e., cracking with a small fractionating column or no fractionating column to produce crude fluoro cyclic trimer overhead followed by a standard distillation to produce high purity fluoro cyclic trimer.
Processes using cracking catalysts to produce cyclic trimer are well known in the art. Catalysts which have traditionally been used in the art are alkali metal compounds, preferably alkali metal hydroxides, including potassium hydroxide (KOH) and sodium hydroxide (NaOH) with octadecanol. Undesirable side reactions that occur under the conditions that produce cyclic trimer using these traditional catalysts include: dehydrohalogenation of the trifluoropropyl groups which produces unsaturated siloxanes; and cleavage of the trifluoropropyl group creating a trifunctional group which reduces yield of the desired cyclic trimer. The NaOH in octadecanol catalyst system causes less of these side reactions than the KOH, but the level of side reactions using NaOH in octadecanol is still undesirable. Additionally, because of the presence of these side reactions, the maximum temperature at which the reaction can be efficiently operated is limited to about 225.degree. C. Further, alkali metal hydroxides cause the dehydrofluorination reaction and the cleavage reaction resulting in the deactivation of the active catalyst which reduces both the reaction rate and the length of the run.